Antenna unit and radio base station therewith

ABSTRACT

Phase and amplitude deviations, which are generated, for example, by cables connecting an array antenna of a CDMA base station and the base station, are calibrated in the baseband. 
     The base station comprises: an antenna apparatus  1 ; couplers  2 ; an RF unit  3  that converts a receive signal to a baseband signal, converts a transmit signal to a radio frequency, and performs power control; an A/D converter  4  for converting a receive signal to a digital signal; a receive beam form unit  6  that multiplies the receive signal by semi-fixed weight; a despreader  7  for this signal input; a time-space demodulator  8  for demodulating user data; a despreader  9  for probe signal; a space modulator  14  for user data; a spreader  13  for user signal; a channel combiner  12 ; a Tx calibrater  11  for controlling calibration of a signal; a D/A converter  10 ; a unit  16  for calculation of correlation matrix for generating a probe signal used for controlling an Rx calibration system and a TX calibration system; a spreader  17  for probe signal; a power control unit  18 ; a D/A converter  19 ; an RF unit  20  for probe signal; an A/D converter  21  for signal from the couplers  2 ; and a despreader  22.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an antenna unit and radio base stationprovided with that antenna unit.

2. Related Art Statement

Recently, demand for the cellular mobile phone of the CDMA (CodeDivision Multiple Access) system is increasing, and with that,techniques of coping with traffic increase are attracting attention. Oneis the technique of adaptive array antenna. In this technique, aradiation pattern of an antenna is controlled to follow each of multipaths through which a user signal arrives so as to moderate interferenceby signals of other users.

SUMMARY OF THE INVENTION

There exists a technique in which the control of the radiation patternof an array antenna is carried out in the baseband.

However, a signal subjected to the array antenna controlling in thebaseband must passes through various circuits and cables beforetransmission from the antenna, and accordingly, when the signal arrivesat each antenna, deviation due to distortion is generated betweensignals arriving at respective antennas. Thus, when there is deviationbetween signals arriving at respective antennas, it is impossible totransmit the signal with a desired radiation pattern.

Thus, a baseband processing circuit requires circuits for estimatinglevel deviation and phase deviation generated in a radio frequency unitand cables and for compensating those deviations. Further, when cablelength is large, it expands and contracts owing to variation intemperature, and accordingly, as a compensation circuit, use of anadaptive processing circuit is required.

In the present invention, a probe signal is applied to cables and aradio frequency unit, and an adaptive processing circuit uses this probesignal to perform the above-mentioned compensation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of a radio base stationapparatus according to the present invention;

FIG. 2 is a diagram showing a configuration of a unit for calculation ofcorrelation matrix;

FIG. 3 is a diagram showing a configuration of another radio basestation apparatus according to the present invention;

FIG. 4 is a view for explaining an example of configuration of anantenna apparatus according to the present invention;

FIG. 5 is a view for explaining an example of configuration of anotherantenna apparatus according to the present invention; and

FIG. 6 is a view for explaining an example of configuration of stillanother antenna apparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, in the following, embodiments of a radio base station apparatus andan antenna unit used for that apparatus according to the presentinvention will be described in detail referring to the drawings.

FIG. 1 is a block diagram showing a configuration of a radio basestation apparatus according to an embodiment of the present invention,and FIG. 2 is a block diagram showing a configuration of a unit forcalculation of correlation matrix. In FIGS. 1 and 2 the referencenumeral 1 refers to an antenna apparatus, 2 to a coupler, 3 and 20 toradio frequency units (RF units), 4 and 21 to A/D converters (ADC), 6 toa receive beam (Rx beam) form unit, 7 and 22 to despreaders, 8 to aspace-time demodulator, 9 to a despreader for probe signal, 10 and 19 toD/A converters (DAC), 11 to a Transmit calibrater (Tx calibrater), 12 toa channel combiner, 13 to a spreader, 14 to a space-time modulator, 15to a spreader for probe signal, 16 to a unit for calculation ofcorrelation matrix, 17 to a spreader for probe signal, 18 to a powercontrol unit, 23 to a signal input line, 24 to a multiplexer, 25 to aconjugate calculator, 26 to a delay device, 27 to a multiplier, and 28to a memory.

Generally, in order to expand coverage of a cell as a communication areain mobile communication, an antenna is installed on a high steel toweror a rooftop of a building, being separated from a main part (an RFunit, a baseband unit, a control unit, etc.) of a base station.Accordingly, it is necessary to draw cables several ten meters long, andthus, it is difficult to keep phase relation between signals ofrespective antenna systems in their transmission. Further, the RF unitconstituting the base station amplifies signals by amplifiers, and it isdifficult to amplify signals while uniformly maintaining the noisefigure (NF) and amplitude of respective systems. Thus, it is necessaryto provide the base station with a unit that compensates the level andphase in some way.

With respect to a receiving system of the base station apparatus, it isnot necessary to compensate the level and phase as mentioned above, aslong as an adaptive array antenna is employed. This is because, in theprocess of realizing the optimum array weight control, phase deviationand level deviation are compensated automatically. On the other hand, ina transmission system, control of array weight is performed based on thearray weight estimated in the receiving system as uplink, andaccordingly, the system requires a mechanism for compensating the leveland phase deviations generated in the receiving system and the level andphase deviations generated in the transmission system. The control ofarray weight is performed individually for each user, and thus, in thecase of a CDMA system, array control in a baseband is desirable. Thus,it is necessary to maintain amplitude relation and phase relation ofsignals generated from baseband signals when they are transmitted froman antenna.

As technical literature relating to control of an adaptive arrayantenna, may be mentioned an article, “1999 General Convention of theInstitute of Electronics, Information and Communication Engineers,B-4-41”, which is incorporated herein by reference.

A radio base station apparatus as an object of the embodiments of thepresent invention employs the CDMA system as a radio communicationsystem, and uses an array antenna so that it can reduce interferencebetween channels and increase channel capacity. The radio base stationapparatus is constructed to include a receive calibration system (Rxcalibration system) and a transmit calibration system (Tx calibrationsystem). One of these systems may be used in certain embodiments, whichare included in the scope of the present invention. However, to realizethe Tx calibration system, both the Rx calibration system and Txcalibration system are required.

As shown in FIG. 1, a radio base station apparatus according to oneembodiment of the present invention comprises: an antenna apparatus 1consisting of a plurality of antenna elements 1; couplers 2 respectivelyprovided in the neighborhoods of terminals of the antenna elements onthe side of the base station apparatus; an RF unit 3 that converts areceived signal to a baseband signal, converts a transmission signal toa radio frequency, and performs power control; an A/D converter 4 thatconverts the received baseband signal to a digital signal; an Rx beamform unit 6 that multiplies the digitized received signal by pre-setweight; a despreader 7 that despreads this signal; a time-spacedemodulator 8 that demodulates the despread signal to obtain user data;a despreader 9 for probe signal, that despreds the output signal of theAID converter 4; a time-space modulator 14 that modulates user data; aspreader 13 that spreads this user data; a channel combiner 12 thatperforms channel combining with respect to signals from the spreader 13;a Tx calibrater 11 that controls signal calibration according to thepresent invention: a D/A converter 10 that converts a digital signalfrom the calibrater 11 to an analog signal to send it to the RF unit 3;a unit 16 for calculation of correlation matrix, that produces a probesignal for controlling the Rx calibration system and the Tx calibrationsystem, and calculates calibration required for phase and amplitudecalibration of a received signal; a spreader 17 that spreads the probesignal; a power control unit 18 that controls power of the probe signal:a D/A converter 19 that converts the probe signal to a digital signal;an RF unit 20 that has the equivalent function as the RF unit 3, inputsthe probe signal to the couplers 2 and converts signals from thecouplers 2 to digital signals; a despreader 22 that despreads thosesignals, and a spreader 15. The spreader 15 is a circuit whichspread-modulates a reference signal generated by the correlationcalculation unit 16 with a particular spread code. The reference signalmay be, for example, a signal comprising all zeros.

Next, there will be described the Rx calibration system in the basestation apparatus constructed as described above. In FIG. 1, a signalline shown as a heavy line indicates that, in fact, there exist signallines corresponds to the number of the antenna elements in the antennaapparatus 1. Further, with respect to a component having input andoutput connected to a signal line of a heavy line, it means, in fact,that there exist a plurality of such components corresponding to thenumber of the antenna elements in the antenna apparatus 1.

In the Rx signal calibration system, it is necessary to add the probesignal at terminals of the antennas. In order to minimize effect oncommunication, the added probe signal should be controlled in its power.Phase relation of each pair of the antennas can be obtained bycalculating the correlation with respect to the result of despreadingthe probe signal. When the correlation shows a specific relation, it isassured that the received signals also have a specific relation, andeach deviation of level and phase can be measured.

Accordingly, in the embodiment, the base station apparatus possessingthe array antenna having a plurality of antenna elements comprises: theunit that adds the probe signal to each of received signals received bythe antenna elements of the mentioned array antenna; the probe signaldespreading unit that despreads the mentioned probe signal added to thereceived signals; the calibration calculating unit that calculatescalibration required for calibrating phase and amplitude of eachreceived signal based on the signals from the mentioned despreadingunit; and a unit for calibrating phase and amplitude of the mentionedeach received signal based on the calibration from the mentionedcalibration calculating unit.

In FIG. 1, signals received by the antenna apparatus 1 are mixed by thecouplers 2 with the probe signal separately generated within the basestation. In number, the couplers corresponds to the antenna elements,and the probe signal to be mixed is branched and applied to each antennaelement.

The probe signal is supplied to the couplers 2 through one supply line.Complex amplitude of the probe signal supplied to each antenna elementis decided by the physical relation between the couplers 2 and thesignal supply line. By previously obtaining this relation in a knownenvironment such as a laboratory, the level and phase relation of theprobe signal to be supplied can be known. In an actual field, based onthose known data, it is possible to detect the level and phasedeviations of the signal, which are generated since the signal passesthrough the RF unit 20 and the cable between the couplers 2 and the RFunit 20.

The data that becomes source of the probe signal is a specific signalsuch as an all-0 signal, and produced by the unit for calculation ofcorrelation matrix 16. The produced data is spread by the spreader 17for probe signal. The power of the probe signal must be sufficientlysmall in comparison with other communication signals. This is because,when the power of the probe signal is large, interference by the probesignal largely affects other communication, and reduces the channelcapacity. By this reason, the power control unit 18 keeps the power ofthe probe signal at the necessity minimum. The signal subjected to thepower control is converted to an analog signal by the D/A converter 19.The converted probe signal is subject to frequency conversion and powerconditioning, inputted to the couplers 2 through the supply line, andadded to the received signals from the antenna apparatus 1.

In the meantime, in the CDMA system, peak detection is required fordetecting a phase of the spread code of the received signal. Methods ofrealizing it includes a method in which a signal received by anomni-antenna is used for the peak detection, and a method in which asignal received by one antenna of array antenna is used for the peakdetection. However, in these methods, it may happen that the peakdetection does not work well since the array gain can not be obtainedowing to large interference power when, for example, the number ofconnected channels increases. In order to solve this problem, effectiveis a method of improving a signal-to-interference-power ratio byemploying beam forming with fixed weight to convert signals receivedthrough respective antenna elements (element space) to a group ofindependent beams (beam space).

For this fixed beam forming, it is desirable that beam shapes arevariable in accordance with time selectivity or space selectivity of,for example, traffic or topography, so as to improve peak detectionsensitivity. To this end, it is convenient that the beam form unit forconversion to the beam space operates in the baseband. In thissemi-fixed beam forming, an array response vector adapted for a specificsignal is not obtained, but a given directivity response pattern isrealized by the beam form unit. Thus, it is impossible to produce adesired directivity response pattern when level or phase deviation isgenerated in the cable or the RF unit similarly to the transmissionsystem. Thus, a mechanism for compensating the level and phasedeviations is required.

Now, the received signals, which are received through a plurality ofantenna elements of the antenna apparatus 1 and added with the probesignal, are subjected to frequency conversion in the RF unit 3,converted to baseband signals for respective antenna elements, andfurther converted to digital signals by the A/D converter 4. The signalsconverted to the digital signals by the AID converter 4 are multipliedwith semi-fixed array weight (array response vector) in the beam formunit 6 to be replaced by the beam space having a main beam in a specificdirection of the antenna apparatus 1. At that time, if bit width of thearray weight is sufficient, not only beam forming is performed, but alsothe level and phase deviations generated in the cable and the RF unitcan be calibrated at the same time. This relation can be expressed byEq. 1. $\begin{matrix}\begin{matrix}{x = \quad {W^{H}{Cr}}} \\{= \quad {{\begin{bmatrix}w_{11} & \cdots & w_{11} \\\vdots & ⋰ & \vdots \\w_{11} & \cdots & w_{11}\end{bmatrix}^{H}\begin{bmatrix}c_{1} & \quad & 0 \\\quad & ⋰ & \quad \\0 & \quad & c_{n}\end{bmatrix}}\begin{bmatrix}r_{1} \\\vdots \\r_{n}\end{bmatrix}}} \\{= \quad {Qr}}\end{matrix} & {{Eq}.\quad 1}\end{matrix}$

In Eq. 1, x is a signal vector in the beam space, r is a signal vectorin the element space, and C indicates calibration operation in theelement space. Further, W indicates the conversion operation from theelement space to the beam space. In the third line of the equation, thematrices W and C are expressed unitedly by their product Q. Thisoperation expresses the calibration and array weight operation accordingto the present invention. The beam form unit 6 in FIG. 6 multiplies thereceived signals by the matrix Q in response to a control signal fromthe blow-mentioned unit for calculation of correlation matrix 16 so asto perform unified operation including the beam forming and calibrationof each element. As a result, the signals can be obtained from the beamform unit such that a signal from a specific direction (within theformed beam) is outputted as a larger value. In the present invention,the above-mentioned received signal calibration unit and the beam formunit for the array antenna are put together into one unit in theabove-mentioned radio base station apparatus.

With respect to the signals converted to the beam space, the despreader7 performs peak detection, and performs despreading operation based onthe obtained path phase. As already described, the desired wave signalsthat come to have the space selectivity by the conversion to the beamspace are improved in the signal-to-interference-power ratio, and becomeeasy to perform the peak detection. The signals subjected to thedespreading by the despreader 7 are returned to a user signal by thespace-time demodulator 8 as a decoding unit. The user signal demodulatedby the decoding by the space-time demodulator 8 is one that is obtainedby combining the signals spread in the space and time directions withsuitable weight to obtain diversity effect.

Calibration information used in the above-mentioned beam form unit 6 canbe obtained by the procedure described in the following.

The signals that have been converted to the digital signals by the A/Dconverter 4 still have the level and phase deviations generated in eachantenna element. The despreader 9 extracts these level and phasedeviations and performs despreading operation on the probe signalincluded in the signals. The signals extracted from the despreader 9 bythis operation are the probe signals applied to the terminals ofrespective antenna elements, added with the level and phase deviationsgenerated in the RF unit 3 and the cables connecting the couplers 2 andthe RF unit 3. The output signals of the probe signal despreader 9 areapplied to the unit 16 for calculation of correlation matrix, to be usedfor preparing a correlation matrix for extracting level and phaserelations.

The unit 16 for calculation of correlation matrix obtains thecorrelation matrix based on the signals from the probe signal despreader9. The obtained correlation matrix is the sum of a signal subspace andan interference subspace. The interference subspace becomes an errorfactor when other communications have space selectivity, and it isdesirable to delete the interference subspace. The interference subspacecan be obtained by performing spread intentionally using a spreadingcode that has not been used and by obtaining a similar correlationmatrix based on the result of spreading. As shown in Eq. 2 the mentionedinterference subspace can be obtained as a signal subspace A bysubtracting the correlation matrix I that is obtained by performingdespread intentionally using the nonuse spreading code, from acorrelation matrix S that is obtained by using a spreading code adaptedfor the probe signal. $\begin{matrix}{A = {{S - I} = {\begin{bmatrix}S_{11} & \cdots & S_{1n} \\\vdots & ⋰ & \vdots \\S_{n1} & \cdots & S_{nn}\end{bmatrix} - \begin{bmatrix}i_{11} & \cdots & i_{1n} \\\vdots & ⋰ & \vdots \\i_{n1} & \cdots & i_{nn}\end{bmatrix}}}} & {{Eq}.\quad 2}\end{matrix}$

Element space signature is obtained as the information obtained bycalculating an eigen vector having the maximum eigen value from theobtained signal subspace A. This information indicates in which leveland phase relation the signal applied in the element space is recived.The obtained information should be a value (target) predetermined by thetopology of the antenna and the coupling relation of the system to whichthe probe signal is applied. The discrepancy between the measured valueand the target becomes the calibration. As the correlation matrix(target) that should be obtained in advance, can be used measurementobtained when the array pattern is adjusted to desired characteristicsin a special measurement environment such as an anechoic chamber. Byusing this measurement as the target to obtain the calibration matrix C,it is possible to reproduce the desired array pattern even in an actualenvironment.

Next, a method of obtaining the calibration will be described. Eq. 3 isa matrix indicating the probe signal subspace A measured in advance in alaboratory etc. when the level deviation and the phase deviation owingto the cable and the RF unit do not exit or are calibrated. The eigenvector cc with the maximum eigen value can be obtained from the matrixA. Eq. 4 shows that a is an eigen vector of the matrix A.$\begin{matrix}{A = \begin{bmatrix}a_{11} & \cdots & a_{1n} \\\vdots & ⋰ & \vdots \\a_{n1} & \cdots & a_{nn}\end{bmatrix}} & {{Eq}.\quad 3}\end{matrix}$

$\begin{matrix}{\alpha = {{{eig}(A)} = \begin{bmatrix}\alpha_{1} \\\vdots \\\alpha_{n}\end{bmatrix}}} & {{Eq}.\quad 4}\end{matrix}$

The operation eig in FIG. 4 means a function for extracting the eigenvector having the maximum eigen value. On the other hand. a signalsubspace B measured in the actual environment is shown in Eq. 5 Alsowith respect to the matrix B, the eigen vector having the maximum eigenvalue can be obtained by the similar calculation. Eq. 6 shows the eigenvector β of the matrix B. And, the calibration matrix of the elementspace can be obtained by Eq. 7. $\begin{matrix}{B = \begin{bmatrix}b_{11} & \cdots & b_{1n} \\\vdots & ⋰ & \vdots \\b_{n1} & \cdots & b_{nn}\end{bmatrix}} & {{Eq}.\quad 5} \\{\beta = {{{eig}(B)} = \begin{bmatrix}\beta_{1} \\\vdots \\\beta_{n}\end{bmatrix}}} & {{Eq}.\quad 6} \\{C = {\begin{bmatrix}c_{1} & \quad & 0 \\\quad & ⋰ & \quad \\0 & \quad & c_{n}\end{bmatrix} = \begin{bmatrix}{\beta_{1}/\alpha_{1}} & \quad & 0 \\\quad & ⋰ & \quad \\0 & \quad & {\beta_{n}/\alpha_{n}}\end{bmatrix}}} & {{Eq}.\quad 7}\end{matrix}$

When the calibration matrix C is obtained, the array control methodshown in FIG. 1 can perform the conversion from the element space to thebeam space and the calibration of the level and phase deviations in theelement space, at the same time.

As an important point here, the probe signal applied at the terminals ofthe antenna does not pass through the propagation path and accordinglyis not affected by fading and the information of the probe signal isknown. Owing to this, the despreading operation can be performed easily.As another important point, the generation and reception of the probesignal is performed in the same or adjacent apparatuses. Owing to this,it is possible to commonly use a local oscillator used for frequencyconversion and timing generation in the RF unit.

Since the present embodiment of the invention has the above-describedconfiguration, it is possible to easily realize in-phase addition in avery long time without generating a frequency error and timing error.Further, variations of the phase and amplitude generated in the cableand the RF unit are very slow in comparison with the chip rate of thereceived signals, and it does not practically become problem to spend along measuring time for estimating the correlation matrix. Accordingly,by increasing the spreading rate, effect of the probe signal on theother communications can be made very small. Signal strength of theprobe signal can be known by the diagonal elements of the signalsubspace. By controlling the power control unit 18 such that thediagonal elements give sufficient signal strength although not largerthan the necessary, the effect of the probe signal on the othercommunications can be made very small. Further, in the above-describedembodiment of the present invention, the level and phase deviations ofeach system are calibrated in the baseband unit. This can decreasecalibration operation and production costs.

In the above-described embodiment of the present invention, is describedthe configuration in which signals from a plurality of antenna elementsare despread at the same time for obtaining the signal subspace.However, calibration cycle of the calibration matrix is sufficientlyslow in comparison with the spreading rate, the calibration matrix canbe updated by time sharing processing.

FIG. 2 shows circuit structure of the unit 16 for calculation ofcorrelation matrix for the case that the calibration matrix is generatedby the time sharing processing. In the following, this will bedescribed. The unit 16 for calculation of correlation matrix of thisexample comprises a multiplexer 24, a conjugate calculator 25, aplurality of delay devices 26, a plurality of multipliers 27, and aplurality of memories 28.

In FIG. 2, signals inputted to signal input lines 23 are signals fromthe respective antenna elements, signals from the despreader 9 for probesignal, shown in FIG. 1, the probe signals applied to the terminals ofthe respective antenna elements, and the level and phase deviationsapplied in the RF unit and in the cables between the couplers 2 and theRF unit 3. In the shown case, the multiplexer 24 has a function oftimesharing six input signals one by one.

The signals outputted serially in time sharing from the multiplexer 24are inputted into the conjugate calculator 25 and into the multipliers27 that are connected to the output sides of the conjugate calculator 25and the serially-connected delay devices 26. The delay devices 26operate synchronously with the multiplexer 24, and accordingly themultipliers 27 performs calculation of correlation between the signalsdelayed by the delay devices 26 and the just-inputted signal.

The results of this operation are accumulated in the memories 28. As aresult, at a point of time when time-division multiplexing correspondingto six devices is finished in the multiplexer 24, the correlation matrixis accumulated in the memories 28. This information accumulated in thememories 28 is delivered to the beam form unit 6 of FIG. 1, to besubjected to the weight calibration processing in the baseband accordingto the present invention. Further, if necessary, contents accumulated inthe memories 28 can be used after further averaging processing. In thatcase, precision of the calibration can be improved.

Next, the transmission system in the base station apparatus constructedas shown in FIG. 1 will be described. The Tx calibration system shouldadd the probe signal to transmission signals in the baseband unit, andextract the signals from the terminals of the antennas. It is necessaryto perform investigation on one antenna system (element) out of aplurality of antenna terminals. This investigation can be performed suchthat: (1) one of signals to a plurality of antenna systems is selectedin the baseband, and the probe signal is applied to that signal; (2)signals extracted from the antenna terminals are subjected todespreading, to investigate response of each antenna system by timesharing; and (3) correlation is calculated on the result of despreading.When the correlation indicates a specific relation, it is assured thatreceived signals are also in the specific relation, and each of thelevel and phase deviations can be measured.

According to the present embodiment, in the above-mentionedconfiguration, the RF unit that converts the mentioned received signalsto baseband signals has a function of converting the signals, which havebeen subjected to the D/A conversion, to radio frequencies so as toinput them into the respective antenna elements; the mentioned couplershave a function of extracting a part of transmission signal inputtedinto each of antenna elements; and the mentioned probe signal RF unithas a function of converting the signals from the mentioned couplers tobaseband signals. Further, the present embodiment comprises: thespreader for Tx probe signal, which spreads a specific code series usinga specific spread code; the Tx signal calibrater that calibratestransmission signals generated in the modulator by the signals from thementioned unit for calculation of correlation matrix; the Tx signalcombiner that adds the output signal of the mentioned spreader for Txprobe signal to only a signal to be transmitted from one antenna elementout of the signals generated by the mentioned calibrater, so as togenerate a transmission signal added with probe; the D/A converter thatconverts the output of the mentioned Tx signal combiner from a digitalsignal to an analog signal and inputs the converted signal to thementioned RF unit that converts received signals to baseband signals;the A/D converter for probe signal that performs conversion from ananalog signal to a digital signal on the signals that are received fromthe mentioned couplers and have been converted to the baseband signalsin the mentioned probe signal RF unit; and the despreader for Tx probesignal that despreads the output of the mentioned AID converter forprobe signal using the spread code of the Tx probe signal so as to inputthe result to the mentioned unit for calculation of correlation matrix.The mentioned unit for calculation of correlation matrix is providedwith the Tx signal calibration system that obtains correlation of Txprobe signals between each pair of the antennas based on the output ofthe despreader for Tx probe signal and calculates quantity of phaserotation and quantity of amplitude calibration required for realizing aspecific relation between the eigen vector having the maximum eigenvalue decided from the obtained correlation matrix and a predeterminedvector, so as to control the calibration by the mentioned calibrater.

In FIG. 1, prepared user data is subjected to space modulation by thespace modulator 14. The space modulator means a modulation circuit thatadditionally contains operations for giving a suitable phase andamplitude to each antenna element in order to form a beam, in comparisonwith an ordinary modulation circuit. Information of a user is spread bythe spreader 13 using a spread code that is different for each user. Thespread data is added in the channel combiner 12 to be aggregated toinformation corresponding to the number of the antenna elements. Thesignal aggregated to the number of the antenna elements is subject topre-calibration in the calibrater 11 based on the signal from the unit16 for calculation of correlation matrix, with respect to the leveldeviation and phase rotation that are to be generated in the cables,amplifiers, etc. The calibrated signal is converted to an analog signalin the D/A converter 10 subjected to up-conversion and poweramplification in the RF unit 3 and inputted to each antenna element, tobe transmitted from the antenna apparatus 2.

The method of obtaining the calibration vector for transmission signalsin the unit 16 for calculation of correlation matrix is generallysimilar to the above-described case of the receiving system.

Namely, a reference signal (for example, a signal of all-0) generated inthe correlation calculation unit 16 is spread with a specific spreadcode by the spreader 15. The spread signal is added to a signal linecorresponding to each antenna element, between the calibrater 11 and theD/A converter 10. In this operation, the signal is not distributed toall the antenna elements at the same time but added to each signal lineone after another by time-sharing. By this, a receiving side can clearlydistinguish an antenna element that transmitted the received signal.

Here, the Tx probe signal is mixed to a specific antenna bytime-sharing. However, the Tx probe signal may be added at the sametime, by changing the spread code for the Tx probe signal for eachantenna element. Namely, it is simply that signals applied to therespective antenna elements are spread by respective spread codes. Inthis case, however, interference given by the measurement systemincreases, being multiplied by the number of the antenna elements.

At the terminal of each antenna element, is provided the coupler 2, andthe coupler 2 extracts a part of the signal transmitted. The extractedsignal is down-converted by the RF unit 20. Thereafter, the signal fromthe RF unit 20 is converted to a digital signal by the A/D converter 21,and the converted signal is despread by the despreader 22 to be inputtedto the unit 16 for calculation of correlation matrix. The unit 16 forcalculation of correlation matrix calculates the calibration matrix C bythe method shown by the above-described Eqs. 1-7. The calculatedcalibration matrix C is inputted to the calibrater 11 for calibration ofthe transmission signal.

The above-described embodiment of the present invention can alsocalibrate the amplitude and phase deviations owing to the cables,amplifiers, etc. in the transmission system.

Further, in order to decrease the effect of the probe signal, it isnecessary to increase the spreading rate. When the same local oscillatoris used both the generating and receiving units for the probe signal, itis possible to decrease synchronization errors and to decrease circuitsrequired for synchronization. Since the generating unit and thereceiving unit for the probe signal exist very closely to each other, itis not difficult to commonly use the local oscillator. Thus, in thepresent embodiment, in the above-described radio base station apparatus,the mentioned Rx signal calibration system and Tx signal calibrationsystem use the same local oscillator as an oscillation source to performup-conversion and down-conversion, and to perform timing generation.

The radio base station apparatus according to thus-described embodimentof the present invention has been described as one in which the RF units3 and 20 of FIG. 1 use the same local oscillator. However, according tothe present invention, these RF units 3 and 20 may use different localoscillators, and, in that case, the AFC (Auto Frequency Control)function may be used to obtain spread gain.

FIG. 3 is a block diagram showing a configuration of a radio basestation apparatus according to another embodiment of the presentinvention, and it will be described in the following. In FIG. 3, thereference numeral 5 refers to a calibrater and the other symbols aresame as in FIG. 1.

The embodiment shown in FIG. 3 is different from the embodiment shown inFIG. 1 in that the beam form unit 6 for the Rx calibration system isseparated into a beam form unit 6 and the calibrater 5, that the pointfor extracting the probe signal is an output terminal of the calibrater5 and that the signal obtained by spreading the reference signal of theTx calibration system is inputted to an output terminal of the spreader13. In such structure, the results of a series of operations on thesignals are not changed, and the results similar to FIG. 1 are obtained.

In the above-described embodiment, the probe signal is spread by thespreaders 15 and 17. However, since the other signals are spread, it isnot necessary to spread the probe signal in order to separate it fromthe other communications. In other words, it is because the probe signalcan be considered as a signal spread by a signal of all-0. Thus, theabove-described embodiment of the present invention can dispense withthe spreaders 15 and 17, which simplifies the apparatus. When a carrierleak of the base station apparatus is sufficiently small andinterference from the other communication systems is small, then, a sinewave may be used as the probe signal.

However, when there is a carrier leak in the radio base stationapparatus or when there are other communication systems and manyundesired signals exist in the carrier frequency, then, omission of thespreaders 15 and 17 may lower the performance.

FIGS. 4-6 are views for explaining examples of configuration of anantenna apparatus according to embodiments of the present invention,and, now, structure of the antenna will be described in the following.In FIGS. 4-6 the reference numeral 29 refers to an antenna element, 30to a signal line, 31 to a probe signal line, 32 to a radiating element,33, 34 and 37 to probe signal elements, and 38-40 to array antennas.

The above-described embodiments of the present invention have beendescribed as ones in which the couplers are provided in the subsequentstage of the antenna terminals. However, when the target is to beobtained in a test in an anechoic chamber or the like, it is convenientthat a coupler is contained in an antenna itself. The antenna apparatusof the embodiment shown in FIG. 4 is an array antenna that comprises aplurality of antenna elements 29. The signal lines 30 connected to theterminals of the antenna elements 29 are connected to the RF unit 3, andthe probe signal line 31 is connected to the RF unit 20.

Within a circle, is shown an enlarged view of parts constituting acoupler 2. The coupler 2 comprises a probe signal element 33 consistingof a piece of metal that is in weak conjunction with a radiating element32 connected to a signal line for each antenna element 29. The signalline 31 is connected to this probe signal element 33. It is sufficientthat the terminal of the antenna element 29 to which the signal line 30is connected and the terminal of the probe signal element 33 to whichthe probe signal line 31 is connected are in weak conjunction with eachother at isolation of about 20 dB.

The antenna apparatus shown in FIG. 4 according to the embodiment of thepresent invention can be constructed such that the antenna apparatus 1and the couplers 2 are unified. Thus, the convenient antenna apparatuscan be constructed.

FIG. 5 shows structure of an antenna apparatus according to anotherembodiment of the present invention. This antenna apparatus is an arrayantenna similar to one shown in FIG. 4. In this antenna apparatus, apart constituting a coupler 2 is constructed such that a probe signalelement 34 as an antenna element for radiation of the probe signal isprovided in the neighborhood of a plurality of antenna elements 29 incommon. Even when the coupling element is arranged in space asdescribed, can be obtained an effect similar to the case describedreferring to FIG. 4 in which input and output of signal is carried outthrough the weak conjunction with the radiating element of the antenna.

FIG. 6 shows a configuration of an antenna apparatus according to stillanother embodiment of the present invention.

This antenna apparatus is an example of an antenna apparatus constructedsuch that a plurality of array antennas described referring to FIG. 5and a radiating element for probe.

The antenna apparatus shown in FIG. 6 is constructed such that the arrayantennas 38-40 are arranged in an equilateral triangle to form atriangular prism and a probe signal element 37 is provided in thecentral portion of the triangular prism. In the example shown in FIG. 6,each array antenna corresponding to a side of the triangle comprises abottom board (reflecting element) 38′-40′ and a radiating element38″-40″ arranged on the surface of the bottom board. In this embodiment,the probe signal element 37 is arranged in the center of the cavityenclosed by the array antennas 38-40. Thus, although the distancebetween the array antennas and the probe signal element is short, theirconjunction becomes weak owing to the existence of the reflectingplates. Further, whole surface of each array antenna is covered with areflecting plate, and accordingly, interference power that signal powerradiated by the probe antenna gives to another communication can be madesmall.

The antenna apparatus described referring to FIG. 6 is constructed suchthat the array antennas are arranged into a triangular prism. However,according to the present invention, a plurality of array antennas orantenna elements may be arranged in a shape of a polygon, or antennaelements may be arranged into a cylinder. In that case, when the probesignal element exists inside the polygon or cylinder made by the arrayantennas, similar effect can be obtained.

As described above, according to the present invention, it is possibleto provide a radio base station apparatus in which amplitude and phasedeviations of signals generated to an array antenna owing to cablesconnected to the base station apparatus and amplifiers within the basestation apparatus can be calibrated in the baseband. In addition, anantenna apparatus that is suitable for use in combination with this basestation can be provided. When these apparatuses are applied to acommunication system according to the CDMA system, interference powergiven to other communications can be suppressed to be small.

What is claimed is:
 1. A radio base station apparatus provided with anarray antenna having a plurality of antenna elements, wherein: a receivesignal calibration system of said radio base station apparatuscomprises: a receive probe signal spreading unit which spreads aspecific code series with a specific spread code; a power control unitwhich performs power control on an output signal of said receive probesignal spreading unit; a D/A converting unit for the receive probesignal, for converting an output signal of said power control unit froma digital signal to an analog signal; a probe signal RF unit whichconverts an output signal of said D/A converting unit to a radiofrequency and performs power control on said radio frequency; a couplingunit which adds said probe signal to receive signals receivedrespectively by said plurality of antenna elements, so as to generatereceive signals added with probe; an RF unit which converts the receivesignals added with probe, which are generated in said coupling unit, tobaseband signals; an A/D converting unit which converts the basebandsignals generated in said RF unit to digital signals; a receive probesignal despreading unit which outputs results of despreading the signalssubjected to said A/D conversion with a spread code used for the probesignal, and which outputs results of despreading said signalsintentionally with a spread code that has not been used; a correlationmatrix calculation unit that obtains correlation of receive probesignals between each pair of antenna elements from the output of saidreceive probe signal despreading unit, calculates a signal subspace froman obtained correlation matrix, and calculates phase rotation andamplitude calibration required for an eigen vector having a maximumeigen value of the signal subspace and a predetermined vector to have aspecific relation with each other; and a receive signal calibration unitwhich performs calibration of the output signals of the A/D convertingunit, with said output signals being converted from said basebandsignals by the A/D converting unit, and with said calibrationcorresponding to said phase rotation and said amplitude calibrationcalculated by said correlation matrix calculation unit; and said powercontrol unit controls power of said probe signal inputted, such that thepower becomes a necessity minimum required for said correlation matrixcalculation unit to calculate the correlation matrix.
 2. The radio basestation apparatus according to claim 1, wherein: said RF unit has afunction of converting the signal subjected to the D/A conversion to aradio frequency and of inputting the converted radio frequency to eachantenna element; said coupling unit has a function of extracting a partof a transmit signal inputted to each antenna element; and said probesignal RF unit has a function of converting a signal from said couplingunit to a baseband signal.
 3. The radio base station apparatus accordingto claim 2, wherein: a transmit signal calibration system of said radiobase station apparatus comprises: a transmit probe signal spreading unitwhich spreads a specific code series with a specific spread code; atransmit signal calibration unit which calibrates a transmit signalgenerated in a modulation unit, using signals from said correlationmatrix calculation unit; a transmit signal combining unit whichselectively adds an output signal of said transmit probe signalspreading unit, only to a signal to be transmitted from one antennaelement out of transmit signals generated in said calibration unit, soas to generate transmit signals added with probe; a D/A converting unitwhich converts an output of said transmit signal combining unit fromdigital signals to analog signals and for inputting said analog signalsto said RF unit that converts the receive signals to the basebandsignals; an A/D converting unit for probe signal, for converting ananalog signal to a digital signal, said analog signal being the basebandsignal converted in said probe signal RF unit from the signal from saidcoupling unit; and a transmit probe signal despreading unit whichdespreads an output of said A/D converting unit for probe signal withthe spread code of the transmit probe signal, and for inputting thedepsread output to said correlation matrix calculation unit; and saidcorrelation matrix calculation unit obtains correlation of transmitprobe signals between each pair of antenna elements from the output ofthe transmit probe signal despreading unit, and calculates phaserotation and amplitude calibration required for an eigen vector having amaximum eigen value of an obtained correlation matrix and apredetermined vector to have a specific relation with each other, so asto control calibration by said calibration unit.
 4. The radio basestation apparatus according to claim 3, wherein: said receive signalcalibration system and said treatment signal calibration system use asame local oscillator as an oscillation source to perform up-conversionand down-conversion respectively, and use a same local oscillator as anoscillation source to perform timing generation.
 5. The radio basestation apparatus according to claim 4, wherein: said transmit probesignal is not added selectively to a specific antenna element, but asignal using a different spread code for each antenna element is addedto a signal of each antenna element.
 6. The radio base station apparatusaccording to claim 3, wherein: said transmit probe signal is not addedselectively to a specific antenna element, but a signal using adifferent spread code for each antenna element is added to a signal ofeach antenna element.
 7. The radio base station apparatus according toclaim 3, wherein: said receive signal calibration unit and a beam formunit for the array antenna are formed within a same unit, and saidtransmit signal calibration unit and a beam form unit for the arrayantenna are formed within a same unit.